This invention relates to an improved flexible ceramic tape and method of making same.
The advantage and utility of flexible ceramic tapes are in part measured by the organic content of the binder which holds the ceramic powder together. Prior practice in the ceramic tape industry has been to use polyvinyl butyral as a binder, dioctyl phthalate as a plasticizer and solvents such as the hydrocarbons xylene and toluene and other organic material such as trichlorethylene and alcohol. The difficulty with this prior art practice is that the toxic nature of the solvents requires special solvent scrubber apparatus to prevent the vapor from being expelled into the atmosphere during the drying process. In addition, since these solvents are petroleum derivatives, the price of the solvent has been increasing and its availability is not always assured.
Other tape binder systems used in the past include polyvinyl alcohol with plasticizers such as glycerine, polyethylene glycol and ethylene glycol but the total organic content of such binders including the plasticizer range from 20% to 25% of ceramic dry weight. Because of the high volume to weight ratio of the polyvinyl alcohol in such systems, control of the tape preparation process during the burnout period is very critical, the high organic content tending to produce uncontrolled release of gases which adversely affects the structure and quality of the tape.